1. Field of the Invention
This invention relates to a fluid pump, and more particularly to an electric fluid pump having a cooling system.
2. Description of the Related Art
Referring to FIG. 1, an electric water pump 1 disclosed in U.S. Pat. No. 5,997,261 includes a housing 11. The housing 11 includes a hollow outer housing wall 111, and a partition unit 112 disposed in the outer housing wall 111 and cooperating with the outer housing wall 111 to define an impeller chamber 114, a mounting chamber 115, a cooling chamber 116, a cooling passage 117, and a stator chamber 118 disposed around the cooling chamber 116. The cooling passage 117 is disposed between and in fluid communication with the impeller chamber 114 and the cooling chamber 116.
The electric water pump 1 further includes an impeller 12 disposed in the impeller chamber 114 in the housing 11, a rotor 13 disposed in the cooling chamber 116, a driving shaft 14 co-rotatable with the impeller 12 and the rotor 13, a stator 15 disposed in the stator chamber 118 and aligned with the rotor 13, and an electric control unit 16 disposed in the mounting chamber 115 and electrically connected to the stator 15. The driving shaft 14 has a fluid passage 141 disposed between and in fluid communication with the cooling chamber 116 and the impeller chamber 114.
When the rotor 13 is rotated through operation of the electric control unit 16 to drive rotation of the driving shaft 14 and the impeller 12, a fluid is forced into the impeller chamber 114 through an inlet 119. A major portion of the fluid passes through the impeller chamber 114 along a delivery direction, and is discharged through an outlet 110. A minor portion of the fluid flows through the cooling passage 117 and into the cooling chamber 116. Since the pressure of the fluid located adjacent to the central portion of the impeller 12 is smaller than that of the fluid located adjacent to the circumferential portion of the impeller 12 when the impeller 12 rotates, the fluid returns from the cooling chamber 116 into the impeller chamber 114 through the fluid passage 141 in the driving shaft 14. As a consequence, the fluid flowing into the cooling passage 117 can returns to the impeller chamber 114 through the cooling chamber 116, thereby dissipating heat from the rotor 13, the stator 15, and the electric control unit 16.
The aforesaid electric water pump has a disadvantage. That is, the rate of the fluid flowing through the fluid passage 141 in the driving shaft 14 cannot be changed.
When a change of the cooling effect is desired, it is necessary to adjust the cross-sectional area of the cooling passage 117, thereby resulting in difficulties in manufacture and design. Furthermore, since the minor portion of the fluid flows into the cooling passage 117, when a change of the fluid pressure at the outlet 110 (i.e., output fluid pressure) is desired, it is also necessary to adjust the cross sectional area of the cooling passage 117.